Corona initiation and eventual corona discharge in circuits, for example high power radio frequency (RF) circuits, represents a fundamental power handling limitation. Electric field strengths responsible for corona initiation depend on the material voltage breakdown of the isolating dielectric material(s) used, as well as the circuit geometry and associated dielectric discontinuities. These factors can create electric field strength multipliers which eventually induce corona effects.
Insulating potting compounds have been applied to high voltage circuits or circuit assemblies to improve their ability to withstand higher voltages and thus, higher electric field strengths for reducing detrimental corona effects. Common potting compounds, for example silicon rubber (e.g. MG Chemicals Momentive™ RTV615), have dielectric strengths of about 500 volts per mil (V/mil), with air being 78 V/mil. Methods for preventing corona initiation in circuits requiring even higher voltage handling capability often include increasing the physical size of circuit components, thus maintaining the electric field strengths despite the presence of higher voltages. However, in some applications, the size of relevant components may be restricted for any number of reasons including space constraints and/or performance considerations. One such example includes RF circulators used in modern radar applications, where the thickness of ferrite materials utilized therein cannot be increased indefinitely. In particular, their size may be constrained by the potential for additional modes of propagation within the circulator, which may be destructive or otherwise detrimental to the performance of the circuit.
FIG. 1 provides a simplified cross-section view of an exemplary circulator assembly 10, including ferrites or garnets 12 and associated circuitry 14. During production, these components may be arranged within a hermetically-sealable housing or enclosure 16. A potting compound 18 (e.g. silicon rubber) is used to fill in any void space created within enclosure 16 prior to its sealing. This space includes indicated junction areas A, wherein charged circuitry 14 meets a combination of high and low dielectric materials leading to elevated electric field strengths. As the size of garnets 12 and associated circuitry 14 is constrained for the reasons set forth above, the effectiveness of potting compound 18 is the limiting factor for controlling electric field strengths, and thus, for preventing corona initiation and subsequent discharge.
Alternative solutions for preventing corona effects include constructing circuit assemblies with components having dielectric constants that are nearly equal throughout, mitigating or eliminating electric field strength multiplication factors, and more uniformly distributing the formation of any electric fields. However, these solutions are ineffective for high power RF circulators, as there are currently no potting materials with dielectric constants matching those of the ferrites or garnets (approximately 16) used in circulator applications.
Accordingly, alternative systems and methods for prevention of corona initiation, and circuits utilizing the same, are desired.